Now, reducing the emission of carbon dioxide as a greenhouse effect gas to the atmosphere becomes a pressing need. In order to reduce the emission of carbon dioxide, not only the method of controlling the generation of carbon dioxide itself, but also the method of retaining carbon dioxide under the ground is examined.
A method of retaining a lot of carbon dioxide on a scale of 1 million ton per year under the ground includes the method of infusing carbon dioxide into a stratum. FIG. 9 is a figure showing a conventional carbon dioxide retention apparatus 80. An infusion well 87 being a tube is extended to a retention layer 91 which retains carbon dioxide. The carbon dioxide stored in a carbon dioxide tank 81 is infused in the retention layer 91 by a pump device 83 through the infusion well 87.
In this case, after infusing carbon dioxide in the retention layer 91, it is desirable that carbon dioxide does not extrude to the ground. Therefore, as shown in FIG. 9, a sealing layer 89 which has anticline structure (convex shape to the upper part) is required in the upper part of the retention layer 91. The sealing layer 89 is a stratum which cannot easily pass carbon dioxide, such as clayey layer.
The carbon dioxide infused under the ground does not extrude to the ground by sealing layer 89. However, the stratum which has sealing layer 89 with the upwardly convex shape only exists in the limited places and the suitable place is limited.
Then, as a method also applicable at the place where sealing layer 89 is not anticline structure but monoclinal structure, the method of dissolving carbon dioxide in the stratum water which exists in an underground saltwater aquifer and retaining carbon dioxide efficiently into groundwater is examined.
For example, there is an underground retention method of carbon dioxide which comprises: preparing infusion water by pumping up groundwater of a deep aquifer by a pumping well on the ground; preparing gas-liquid fluid mixture by mixing or dissolving microbubbles of carbon dioxide in the infusion water pressed in the upper part of the infusion well, and pressing the infusion water to the infusion well which reaches the deep aquifer with a pulsating pressure (patent document 1).
Moreover, there is an underground retention system of carbon dioxide gas which uses a carbon dioxide compression apparatus compressing carbon dioxide gas to liquid or supercritical state; compresses a solvent such as sea water by pressurized feeding pump; prepares carbon dioxide dissolving water by dissolving carbon dioxide in the solvent; and presses the generated carbon dioxide dissolving water into the underground aquifer by the infusion well penetrating from the ground to the aquifer (patent document 2).
Moreover, there is an underground retention system of carbon dioxide gas which uses a carbon dioxide compression apparatus compressing carbon dioxide gas to liquid or supercritical state; compresses a solvent such as sea water by pressurized feeding pump; prepares carbon dioxide dissolving water by dissolving carbon dioxide in the solvent; mixes microbubbles of carbon dioxide gas in the generated carbon dioxide dissolving water flowing at the predetermined high velocity, and presses it into the underground aquifer by the infusion well penetrating from the ground to the aquifer (patent document 3).